This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-402004, filed on Dec. 28, 2001; the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a light-emitting device that is able to realize a high luminous efficiency by emitting a light generated in a light-emitting element with a high efficiency, and a method for manufacturing the same.
2. Description of the Related Art
Refractive indices of compound semiconductors constituting light-emitting devices are so high that much luminous energy is lost by reflection at the surface and interface of most of the light-emitting devices and the like. Therefore, it is difficult to emit the light generated within the element to outside. For example, since the compound semiconductor such as gallium phosphide (GaP) has a refractive index of as high as about 3.5, and only about 19% of the light generated in the semiconductor is emitted due to total reflection. For solving this problem, a monolayer with a refractive index of about 1.5 is formed on the surface of the light-emitting element or the like as an antireflective film. However, luminous efficiency is yet insufficient in this type of light-emitting device due to a relatively large refractive index difference between the light-emitting surface and the monolayer film.
It is contemplated to increase transmittance by forming ordered structures with a size of several nanometers on the surface of the light-emitting element, in order to enhance the light emission efficiency (see non-patent document 1 below). However, since it is almost the limit of photolithography even by using a latest eximer laser to form the ordered structure having a refraction preventive effect with a size of several nanometers, the structure should be formed by an electron beam and etching. Consequently, this method is not practically applicable due to its high cost and poor throughput. Moreover, the process for forming the nanometer size of ordered structures has small process window.
Another method known in the art for roughening the light-emitting surface is to treat the surface with hydrochloric acid, sulfuric acid, hydrogen peroxide or a mixed solution thereof (see patent documents 1 and 2 below). However, some crystal faces can be roughened while the other crystal surface cannot be roughened by this method by being affected by crystal orientation of the substrate. Accordingly, the light-emitting surface cannot be always roughened by this some limitations for increasing light emission efficiency.
[Non-patent document 1] Applied Physics Letters, 142, vol. 78, 2001; Jpn. J. Appl. Phys., L735, vol. 139, 2000
[Patent document 1] Japanese Patent Application Laid-open No. 2000-299494
[Patent document 2] Japanese Patent Application Laid-open No. 4-354382
According to a first aspect of the present invention, there is provided a method for manufacturing a light-emitting device comprising: forming a thin film on a surface of the light-emitting element using a resin composition which contains a block copolymer or graft copolymer and forms a microphase-separated structure in a self-organization manner; selectively removing at least one phase of the microphase separated structure of the thin film formed on the surface of the light-emitting element; and etching the surface of the light-emitting element using the remaining phase as an etching mask.
According to a second aspect of the present invention, there is provided a light-emitting element having a finely roughened structure on a surface of an inorganic light permeable layer formed on a surface of the outermost layer of a light-emitting side or on the outermost layer at the light-emitting side of the semiconductor layer constituting the light-emitting element, the surface having a surface property comprising the following two conditions:
(1) the mean radius of gyration  less than R greater than  of projections in the roughened surface structure is {fraction (1/20)} or more and xc2xd or less of the light wavelength, and dispersion "sgr"R of the radius of gyration is 1.05 or more and 2 or less, wherein  less than R greater than  is represented by  less than R greater than =xcexa3R2nR/xcexa3RnR) where nR denotes the number of projections having an arbitrary radius of gyration, and "sgr"R is represented by "sgr"R= less than R greater than /(xcexa3RnR/xcexa3nR) where nR denotes the number of projections having an arbitrary radius of gyration; and
(2) the mean height  less than H greater than  of projections in the roughened surface structure is {fraction (1/10)} or more and 1 or less of the light wavelength, and dispersion "sgr"H of the radius of gyration is 1.05 or more and 2 or less, wherein  less than H greater than  is represented by  less than H greater than =xcexa3H2nH/xcexa3HnH) where nH denotes the number of projections having an arbitrary height, "sgr"H is represented by "sgr"H= less than H greater than /(xcexa3HnH/xcexa3nH) where nH denotes the number of projections having an arbitrary height.